Lighting fixture and light-emitting diode light source assembly

ABSTRACT

An improved LED light source assembly is described, suitable for use as a retrofit for prior lighting fixtures of a kind including a concave reflector, an incandescent lamp positioned with its filament(s) at or near a focal region of the reflector, and a lens assembly for projecting light reflected by the reflector to a distant location, e.g., a theater stage. The improved LED light source assembly includes a compact arrangement of three or more LED assemblies, which are mounted at the forward end of an elongated heat pipe. The heat pipe&#39;s rearward end attaches to a heat sink mountable on the back side of the lighting fixture&#39;s concave reflector, and the heat pipe extends through a central hole in the reflector to position the LED assemblies at or near the concave reflector&#39;s focal region. The concave reflector reflects light emitted by the LED assemblies forward to the lighting fixture&#39;s lens assembly, which in turn projects a beam of light to a distant location. The LED light engine&#39;s configuration allows a significant proportion of the prior lighting fixture to continue to be utilized, leading to substantial cost saving and simplified installation.

CROSS-REFERENCE TO RELATED APPLICATION

Priority is claimed under 35 U.S.C. §119(e) to U.S. ProvisionalApplication No. 61/748,410, filed by David W. Cunningham on Jan. 2,2013, and entitled “Lighting Fixture and Light-Emitting Diode LightSource Assembly.”

BACKGROUND OF THE INVENTION

This invention relates generally to lighting fixtures for theater,architectural and television lighting applications and, moreparticularly, to light source assemblies, or light engines,incorporating light-emitting diodes (“LEDs”) that are configured asretrofit assemblies for attachment to lighting fixtures previouslyincorporating incandescent lamps.

Theater, architectural and television lighting fixtures for projectinghigh-intensity beams of light traditionally have included anincandescent lamp mounted by a burner assembly to a concave reflector,with the lamp's filament(s) located at or near a focal point (or region)of the reflector. A lens assembly is located forward of the lamp andreflector. In use, light emitted by the lamp is reflected in a forwarddirection by the concave reflector, and the lens assembly in turnprojects the reflected light forward along the fixture's longitudinalaxis. One type of these fixtures includes a concave reflector having agenerally ellipsoidal shape, and the lamp filament(s) is/are located ator near the reflector's near focal region. A gate is located at or nearthe reflector's second focal region, and the lens assembly images thelight passing through the gate at a distant location, e.g., a theaterstage. Another type of these fixtures includes a concave reflectorhaving a generally parabolic shape, and the lamp filament(s) is/arelocated at or near the reflector's single focal region. In this case,the lens assembly simply projects the reflected light in a forwarddirection, to bathe, or “wash,” the distant location.

Lighting fixtures of this type have enjoyed widespread use in thetheater, architectural and television lighting fields. Hundreds ofthousands of such fixtures are sold every year. However, because ofrecent advances in the development of high-intensity light-emittingdiodes (“LEDs”), the incorporation of incandescent lamps in suchfixtures is in some cases now considered unduly wasteful of energy. Inaddition, such incandescent fixtures generally require frequentservicing due to the relatively short lifetime of incandescent lamps.Efforts, therefore, have been made to retrofit such lighting fixtures bysubstituting LED arrays for their incandescent lamps.

One effort to configure an LED lighting fixture that utilizes componentsof prior incandescent lamp lighting fixtures is described in U.S. PatentApplication Publication No. 2012/0140463, filed in the name of DavidKinzer et al. The disclosed fixture includes a planar array of LEDsmounted at the rear end of an elongated mixing tube assembly, which inturn is mounted to a conventional gate and lens assembly. The mixingtube assembly includes a reflective inner surface having a convergingsection and diverging section, which function to homogenize the lightemitted by the planar LED array. In use, light from the LED array isdirected through the mixing tube assembly for mixing, and from therethrough the gate and lens assembly for projection toward a distantlocation.

Kinzer's lighting fixture is effective in projecting a high-intensitybeam of light using less electrical power than prior incandescent lamplighting fixtures (30 versus 20 lumens per watt, field efficacy).However, when its design is used as a retrofit of prior incandescentlamp lighting fixtures, it is considered to include an excessive amountof replacement structure and to utilize an unduly small proportion ofthe prior fixtures, i.e., only the gate and lens assemblies of suchprior fixtures. As a retrofit, this design is not considered to beparticularly cost-effective and it cannot be easily installed with thefixture in situ. The Kinzer fixture also has poor soft focuscharacteristics because it images the LED array in the far field.

It should, therefore, be appreciated that there remains a need for amore cost-effective way to retrofit prior incandescent lamp lightingfixtures for use with LED light sources. In particular, there is a needfor an LED light source assembly that can be combined with a greaterproportion of such prior incandescent lamp lighting fixtures. Thepresent invention fulfills this need and provides further relatedadvantages.

SUMMARY OF THE INVENTION

The present invention is embodied in a light source assembly configuredfor attachment to a lighting fixture of a type having a concavereflector and, typically, a lens assembly for projecting light receivedfrom the concave reflector forward along a longitudinal fixture axis.The light source assembly includes three or more light-emitting diode(LED) assemblies; a heat sink; an elongated support having a rearwardend operatively connected to the heat sink and a forward end that mountsthe three or more LED assemblies and that defines a longitudinal lightsource axis; and a fastener assembly configured for attachment to thelighting fixture. When attached to the lighting fixture, the heat sinkis located on the backside of the concave reflector and the forward endof the elongated support extends through the central opening of thereflector, such that the light source axis is substantially aligned withthe fixture axis and the three or more LED assemblies are located at ornear a focal region of the concave reflector. In operation, with thelight source assembly attached to the lighting fixture, light emittedfrom the three or more LED assemblies is reflected by the concavereflector to the lens assembly, which in turn projects the light forwardalong the longitudinal axis, and heat generated by the LED assemblies isconducted rearward along the elongated support to the heat sink.

In one preferred embodiment of the invention, the elongated supportincludes a heat pipe having a single elongated, hermetically sealedinterior cavity extending from the support's forward end to its rearwardend. In this embodiment, the heat pipe preferably includes a graded,sintered powder wick in its interior cavity, the wick having relativelylarge porosity adjacent the heat pipe's rearward end and relatively fineporosity adjacent the heat pipe's forward end. In one form, the heatpipe includes a forward end cap at its forward end and a rearward tubeat its rearward end, which are secured together to form the interiorcavity. The outer surface of the forward end cap defines three or moresubstantially flat surfaces, each sized and configured to support aplanar substrate of a separate one of the three or more LED assemblies.In another form, the elongated support further includes a sleeve havinga central opening sized to fit conformably over the forward end of theheat pipe, the sleeve having an outer surface that defines three or moresubstantially flat surfaces, each sized and configured to support aplanar substrate of a separate one of the LED assemblies.

In another preferred embodiment, the elongated support includes aforward heat pipe and a plurality of rearward heat pipes, each such heatpipe having a forward end and a rearward end. In addition, aheat-transfer block thermally connects the rearward end of the forwardheat pipe to the forward ends of the plurality of rearward heat pipes.The forward end of the forward heat pipe mounts the three or more LEDassemblies, and the rearward ends of the plurality of rearward heatpipes all connect to the heat sink. In addition, the rearward ends ofthe plurality of rearward heat pipes have longitudinal axes arrangedsubstantially parallel with the longitudinal light source axis and theyconnect to the heat sink at spaced-apart locations.

In other, more detailed features of the invention, each of the three ormore LED assemblies includes a plurality of LEDs arranged in one or morerows (preferably two or more rows), with their axes substantiallyparallel with the longitudinal light source axis. When two or more rowsare provided, the LEDs in adjacent rows preferably are arranged in astaggered relationship relative to each other, to improve the far-fieldintegration of the light projected by the fixture. In addition, each ofthe LED assemblies preferably includes a separate light-transmissivedome of silicone (or other material having a high refractive index)disposed over each LED.

In yet other more detailed features of the invention, the three or moreLED assemblies are substantially identical to each other and each mounttheir LED(s) on a substantially planar substrate. The assemblies alsoare arranged substantially symmetrically around the elongated support'sforward end, to improve far-field integration. At least one of the threeor more LED assemblies preferably further includes a temperature sensormounted at the substrate's forward end. Each of the LED assemblies alsopreferably further includes a connector for receiving electrical power,and preferably further includes a light-reflective barrier disposedbetween the connector and the LEDs. Alternatively, each LED assembly canfurther include an electrical connection spaced from the substrate. Inaddition, each LED assembly is bonded to the underlying forward end ofthe elongated support by a layer of conventional solder, thermal epoxy,or, most preferably, a special aluminum/nickel Nanofoil® material, inwhich case the final bonding layer would incorporate aluminum andnickel.

In yet another more detailed feature of the invention, the fastenerassembly for attaching the light source assembly to the lighting fixturecan include a screw sized and configured to engage a threaded socket inthe lighting fixture. The fastener assembly also can include adjustmentmeans for controllably moving the elongated support along the lightingfixture's longitudinal axis, to position the three or more LEDassemblies relative to the focal region of the concave reflector, andthereby adjust the distribution of the projected light.

In still another optional feature of the invention, the heat sinkincludes a plurality of fins and the light source assembly furtherincludes a fan for directing cooling air across the heat sink fins. Thefan preferably extends rearward beyond the rearward end of the elongatedsupport.

In an alternative form, the invention also is embodied in an overalllighting fixture that incorporates a light source assembly having thefeatures summarized above.

Other features and advantages of the invention should become apparentfrom the following description of the preferred embodiment, taken inconjunction with the accompanying drawings, which depict, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view of a lighting fixture embodying theinvention, for projecting a high-intensity beam of light, the lightingfixture incorporating a first LED light engine embodiment.

FIG. 2A is a top front isometric view of the first LED light engineembodiment of the lighting fixture of FIG. 1, the embodiment including asingle heat pipe assembly having a forward end that mounts four evenlyspaced planar arrays of LEDs and a rearward end that is operativelyconnected to a parallel-fin heat sink.

FIG. 2B is a top elevational view of the first LED light engineembodiment of FIG. 2A.

FIG. 2C is a detailed top front isometric view of the four LED arraysmounted at the forward end of the heat pipe assembly of FIG. 2A.

FIG. 2D is a detailed front elevational view of the four LED arraysmounted at the forward end of the heat pipe assembly of FIG. 2C.

FIGS. 3A and 3B are a side elevational view and a side sectional view,respectively, of the heat pipe assembly of FIG. 2A.

FIGS. 4A, 4B, and 4C are a top front isometric view, a side elevationalview, and a rear elevational view, respectively, of the forward end capportion of the heat pipe assembly of FIG. 2A.

FIGS. 5A, 5B, and 5C are a top front isometric view, a top plan view,and a side elevational view, respectively, of one of four identicalarrays of LEDs in the LED light engine embodiment of FIG. 2A.

FIG. 5D is a top front isometric view of one LED array, similar to theisometric view of FIG. 7A, but with the silicone domes overlaying theLEDs removed.

FIG. 6A is a detailed side cross-sectional view of the concave reflectorof the lighting fixture of FIG. 1, with the heat pipe assembly and heatsink assembly of the LED light engine shown in its mounted position.

FIG. 6B is a detailed isometric view of a protective sleeve that mountsin the central opening of the concave reflector in FIG. 6A, to protectthe LED light engine's LED arrays during installation.

FIG. 7A is a top front isometric view of the heat pipe assembly and heatsink assembly portion of a second LED light engine embodiment configuredfor use with the lighting fixture of FIG. 1, in place of the first lightengine embodiment. This second embodiment includes five evenly spacedLED arrays mounted at the forward end of a heat pipe assembly thatincludes a forward heat pipe, four rearward heat pipes, and anintermediate heat-transfer block.

FIGS. 7B, 7C, 7D, and 7E are a front elevational view, a top plan view,a side elevational view, and a rear elevational view, respectively, ofthe second LED light engine embodiment of FIG. 7A.

FIGS. 8A, 8B, and 8C are a top front isometric view, a front elevationalview, and a side elevational view, respectively, of a mounting sleevethat mounts onto the forward end of the heat pipe assembly of FIG. 7Aand that supports five LED arrays in a symmetrical pattern around theheat pipe assembly.

FIGS. 9A, 9B, and 9C are a top front isometric view, a front elevationalview, and a side elevational view, respectively, of the intermediateheat-transfer block that is a part of the second light engine embodimentof FIG. 7A.

FIG. 10A is a schematic cross-sectional view of the layers that are usedto bond the substrate of one LED array to the underlying copper heatpipe, the view being before bonding occurs.

FIG. 10B is a schematic cross-sectional view of the same layers as FIG.10A, but after bonding has occurred.

FIGS. 11A and 11B are schematic views of the light intensity fieldpatterns produced by the lighting fixture of FIG. 1, incorporating anLED light engine in accordance with the invention, adjusted to provide aflat field and a peak field, respectively.

FIG. 12 is a schematic view of the fixed light intensity field patternproduced by a typical prior art lighting fixture incorporating an LEDlight engine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to the accompanying drawings, and particularly toFIGS. 1 and 2A, there is shown a theater lighting fixture 21 forprojecting a beam of light along a longitudinal fixture axis 23 toward adistant location, e.g., a theater stage. The fixture includes a firstembodiment of an LED light engine 25 at its rearward end, asubstantially ellipsoidal reflector 27 for reflecting light emitted bythe LED light engine, and a lens assembly 29 for projecting lightreflected by the reflector. The LED light engine 25 (see FIG. 2A)includes four LED assemblies, or arrays, 31 mounted at the forward endof an elongated heat pipe assembly 33. The LED light engine 25 ismounted behind the backside of the reflector 27, with the heat pipeassembly's forward end projecting through a central opening 35 in thereflector, such that the LED arrays are located substantially at thenear focal region of the reflector's two focal regions. Light emitted bythe LED arrays is reflected by the reflector toward its other, far focalregion, which is located at the rearward end of the lens assembly 29.The lens assembly, in turn, projects the light along the longitudinalfixture axis 23 toward the distant theater stage. In this embodiment,the longitudinal fixture axis is aligned with the central axis of thesubstantially ellipsoidal reflector. As in conventional incandescentlighting fixtures, a gate assembly 37 is located at the site of thereflector's second, far focal region, such that a selected shape orimage can be formed at theater stage.

FIGS. 2A-2D are detailed views of the LED light engine 25 of FIG. 1. Thelight engine includes the elongated heat pipe assembly 33, a heat sinkassembly 39 that connects to the heat pipe assembly's rearward end, anda fan 41 for directing cooling air across the heat sink assembly'sparallel fins 43. The heat pipe assembly, the heat sink assembly, andthe fan all are supported within a cast, or molded, rear housing 45(FIG. 1), which is configured to mate with a cast reflector housing 47of the lighting fixture 21. The rear portion of the heat pipe assembly33 extends perpendicularly through a mid-portion of the heat sinkassembly 39, with a heat-transmissive connection to each of the heatsink's parallel fins 43. The forward end of the heat pipe assemblyprojects forward from the heat sink assembly along a longitudinal lightsource axis 49, and it includes a forward end cap 51 that supports thefour LED arrays 31. This is best shown in FIG. 2C.

When the LED light engine 25 is mounted behind the back side of thereflector 27, the forward end of the heat pipe assembly 33 projectsthrough the reflector's central opening 35 such that the light sourceaxis 49 is aligned with the fixture axis 23 and the LED arrays 31 arelocated substantially at the reflector's near focal region. Electricalcircuitry (not shown) for powering the LED arrays can be located in thespace between the heat sink assembly 39 and the rear housing 45 or,alternatively, in the annular space between the reflector and thereflector housing 47.

FIGS. 3A and 3B are detailed views of the heat pipe assembly 33. Inaddition to the forward end cap 51, the heat pipe assembly includes anelongated rearward tube 53, which is brazed to the end cap's open,rearward end. The end cap and rearward tube both are formed of amaterial having high thermal conductivity, preferably oxygen-free copper(C10100). The rearward tube has a cylindrical cavity extending along itsentire length, and the forward end cap has a cylindrical cavity ofsmaller diameter extending along its length, thus forming a singleelongated cavity. A flange 55 at the forward end cap's open rearward endis configured to mate with the rearward tube's open forward end, tofacilitate a reliable, hermetic connection between the two components.The forward end cap 51 (see FIGS. 4A-4C) preferably is formed bymachining or, alternatively, forging. It includes four planar,rectangular faces 57 of identical size, each configured to support aseparate one of the four LED arrays 31. The flatness of these faces isan important factor in providing a good thermal interface with theoverlaying LED arrays.

A sealing plug 59 is brazed to the rearward end of the rearward tube 53,and a small diameter filling tube 61 seals the forward end of theforward end cap 51. This defines within the heat pipe assembly 33 asingle, elongated, hermetically sealed interior cavity. The sealing plugis approximately aligned with the rearward-most fin 43 of the heat sinkassembly 39, and it can have a range of thickness (˜1 to 6 mm). Athicker plug transmits heat to the rearward-most fin by conduction, andit effectively enables the interior cavity to be shortened, thusenhancing the heat pipe assembly's heat-carrying capacity. The interiorcavity is evacuated to a reduced pressure, and it includes a specifiedamount of a working fluid, preferably deionized water, which isintroduced through the filling tube before the filling tube is sealed bycrimping and brazing.

A copper-powder wick 63 is sintered to the wall of the heat pipeassembly's interior cavity, to enhance the transport of condensed watervia capillary action from the heat pipe assembly's rearward end to itsforward end. Preferably, the copper powder has a graded pore size, withrelatively large pores at the cavity's rearward end and relatively finepores at the cavity's forward end. A boundary line between the largeporosity region and the fine porosity region is represented by thereference numeral 65 in FIG. 3B. Of course, additional levels of poresize gradation also could be provided.

The heat pipe assembly 33 effectively transfers unwanted excess heatgenerated by the four LED arrays 31 backward to the heat sink assembly39 for dissipation. Excess heat generated by the LEDs arrays evaporatesthe working fluid at the heat pipe assembly's forward end, i.e., withinthe forward end cap 51, and the vapor flows rapidly to the heat pipeassembly's rearward end, i.e., in the region of the heat sink assembly,where it condenses to liquid form. The liquid then travels forward alongthe heat pipe assembly's copper powder wick 63 back to the region of theLED arrays. This operation is conventional, and those skilled in the artwill know how to size the heat sink assembly 39 and the fan 41 toproperly handle the amount of heat to be dissipated. Worst caseconditions occur (1) when the lighting fixture 21 is oriented to projectthe light beam in a vertically upward direction, requiring the heat pipeliquid to wick in the same upward direction; (2) when the fixture's gateassembly 37 is closed, reflecting light back via the reflector 27 to theLED arrays 31; and (3) when the fixture's ambient temperature is low,increasing the viscosity of the heat pipe liquid.

In an alternative embodiment (not shown in the drawings), the heat pipecould be formed from just a single tubular component, by swaging itsforward end to a reduced diameter and then soldering onto that forwardend a machined or forged sleeve having a generally polygonal shape, witheach face of the polygon sized to receive a separate LED array.Alternatively, the polygonal shape could be formed by deep-drawing orforging directly into the heat pipe's reduced diameter forward end.Further, the heat pipe could even be substituted by a high-conductivityrod. That latter embodiment is not preferred, however, because itsthermal conductivity and capacity would be sharply reduced.

FIGS. 5A-5D depict one of the four identical LED arrays 31. The depictedarray includes twelve LEDs 67 (FIG. 5D) mounted in two adjacent rows ona rectangular printed circuit board substrate 69. The two adjacent rowsof LEDs 67 are positioned close to the centerline of the substrate 69,so that the LEDs are as close as possible to the longitudinal lightsource axis 49, which aligns with the longitudinal fixture axis 23 whenthe LED light engine 25 is installed. In addition, as best shown in FIG.5B, the LEDs in each row are staggered relative to those in the adjacentrow. A layer of silicone overlays both rows of LEDs, forming atransparent dome 71 over each LED. These domes increase the LEDs'luminous efficacy and help to integrate the light emitted by the LEDs,thereby enhancing the distribution of light in the projected beam.

The substrate 69 is sized to fit over one of the four planar,rectangular faces 57 of the forward end cap 51 of the heat pipe assembly33. Each substrate may overhang one side of its underlying face (as bestshown in FIG. 2D), to increase the electrical isolation between theconductive traces and the heat pipe assembly. The substrates preferablyare formed of aluminum nitride or, alternatively, copper with a thin,dielectric layer having high heat conductivity.

A temperature sensor in the form of an NTC (negative temperaturecoefficient) thermistor 73 is mounted at the forward end of thesubstrate 69. This thermistor has a resistance whose value varies withtemperature, and a measurement of this resistance is used by a controlsystem (not shown) to monitor the LED array's temperature and preventexcessive overheating. The thermistor preferably is located at thesubstrate's forward end, which is the site where an excessive thermalload could initially bring about a partial “dry out” of the heat pipeassembly's working fluid, i.e., deionized water, and thus cause a rapidrise in temperature. The thermistor need be mounted on only one of thefour LED arrays 31, although additional thermistors could be providedfor redundancy.

An electrical connector 75 is mounted at the base end of the substrate69, to receive a mating connector (not shown) that delivers electricalpower to the LEDs 67 and that transmits back to the control system asignal representing the resistance value measured by the thermistor 73.Just a single four-wire cable (not shown) is required, with short jumpercables (not shown) interconnecting the four LED arrays 31. The LEDs ofthe four arrays all are connected in series with each other, so thepower line in the four-wire cable connects to the connector on a firstof the arrays, and each array in succession receives its power via ajumper cable connected to the previous array. Return power is providedto the four-wire cable from the connector on the last of the fourarrays. Two wires in the cable for carrying the temperature measurementvalue can connect to whichever of the four arrays carries the thermistor73. A connector of this kind is preferred to a conventional solderedwire or preformed connection, which could damage the adjacent LEDs withsolder flux during attachment.

A light-reflective thermal barrier (not shown in the drawings) can bepositioned between the LEDs 67 and the connector 75, to reduce theconnector's absorption of light, which could lead to its prematurefailure. One suitable material for such a thermal barrier is aluminumoxide, having a theoretical density of about 94-99%.

Further, suitable alternatives to the use of the connector 75 includethe use of wire-wrap posts, insulation displacement connectors, andlocalized soldering, e.g., soldering to the remote ends of L-shapedpreforms. All of these alternative approaches space the electricalconnection from the underlying substrate.

The twelve LEDs 67 in each LED array 31 are configured to emitsubstantially white light, or colored light, in a generally Lambertianpattern, such that the arrays combine to emit light in a generallyuniform circumferential pattern. This feature, coupled with thestaggering of the LEDs in adjacent rows and the silicone domes 71,cooperate with the conventional circumferential faceting in thereflector 27 to help ensure that the projected beam has an intensitythat is substantially uniform circumferentially and is devoid of darkareas. Alternatively, the LEDs in adjacent rows could have two or moredifferent white light color temperatures and/or colors, which would beintegrated by the reflector facets.

In the particular case of the Source Four® incandescent lighting fixturesold by Electronic Theatre Controls, Inc., of Middleton, Wis., thereflector's facets are sized to blend light emitted by lamp filamentsspaced apart from each other by about 4.0 mm. These same facets shouldbe equally effective in blending light emitted by the LED arrays 31 ifthe spacing between the LEDs 67 of adjacent arrays is no more than 4.0mm, edge-to-edge.

In an alternative embodiment (not shown in the drawings), multiplearrays of LEDs could be mounted on just a single, non-planar printedcircuit board substrate. In that embodiment, each array emits lighthaving a peak intensity substantially perpendicular to the array, andthe multiple arrays are oriented relative to each other such that theycombine to emit light in a circumferential pattern that is substantiallyuniform.

The fan 41(FIG. 2B) is shown to extend rearward of the rearward-most fin43 of the heat sink assembly 39. Airflow is blocked for this portion ofthe fan, without detracting significantly from the fan's effectiveness.This allows the heat pipe assembly 33 to be shortened, thus enhancingits thermal capacity (as discussed below).

The fan 41 is depicted as being located on the lower side of the heatsink assembly 39, for directing cooling air through the parallel fins43. Other orientations for the fan could alternatively be provided. Inaddition, in an alternative embodiment not shown in the drawings, alarger heat sink assembly could be used to eliminate the need for a fan.Other methods of forced-air cooling also could be used, includingsynthetic jets (e.g., Nuventix SynJet products). The heat sink alsocould be configured to extend forwardly into the annular space betweenthe lighting fixture's concave reflector and reflector housing.

With reference again to FIG. 1, it can be seen that the LED light engine25 attaches near the back side of the lighting fixture's reflector 27using a single elongated machine screw 77. The screw engages a threadedsocket 79 formed in the cast reflector housing 47. This is the samesocket as is used to attach an incandescent lamp light engine previouslyused with the fixture 21. Holes 81 (see FIG. 2A) are formed in theparallel fins 43 of the heat sink assembly 39, to accommodate the screw.Triangular-shaped cutouts in the forward-most fins of the heat sinkassembly (see FIG. 2A) provide a nesting fit with structure supportingthe backside of the reflector and minimize air leakage from the heatsink assembly 39. In addition, the LED light engine's rear housing 45 isspecially configured to mate with the fixture's cast reflector housing47, so as to minimize the rearward escape of stray light emitted by theLED arrays 31. Those skilled in the art will appreciate that manyalternative techniques for attaching the LED light engine to thereflector and reflector housing also could be used.

It is important to note that the only new structure in the lightingfixture 21 of FIG. 1 is the LED light engine 25. The remainingstructure, including the reflector 27, the gate assembly 37, and thelens assembly 29, all is of conventional design, used with anincandescent lamp. Moreover, the LED light engine 25 can be attached asa retrofit to a conventional incandescent lamp lighting fixture, simplyby substituting it for the prior incandescent lamp light engine. Thismakes the LED light engine an easily installed, economically viablealternative to the LED lighting fixture described in the Kinzer patentapplication publication identified above.

When installing the LED light engine 25 as a retrofit in the lightingfixture 21 of FIG. 1, or when simply substituting a new LED light enginefor a previous one that has failed, it is important to avoid damagingthe LEDs 67 and silicone domes 71 in the four LED arrays 31. This is aparticular issue when they are being inserted through the centralopening 35 in the fixture's reflector 27, which can be highly abrasivefrom having been drilled out. To this end, and as shown in FIGS. 6A-6B,a protective sleeve 85 is first placed into the opening. The sleeve isformed of nylon, Teflon, or other soft material, and it includesconventional spring tabs 89 to facilitate a snap fit. To provide evenfurther protection for the LEDs and the silicone domes, the frontperiphery of the heat sink assembly 39 could carry an annular guidepanel (not shown) configured to engage portions of the reflector housing47 and thereby provide a coarse centering of the heat pipe assembly 33relative to the reflector's central opening 35 during installation.

With reference now to FIGS. 7A-7E, there is shown a second embodiment ofan LED light engine 89 that can be mounted at the rearward end of thelighting fixture 21 of FIG. 1, in place of its original incandescentlamp light engine (not shown). This second embodiment includes five LEDarrays 31, a heat pipe assembly 91, a heat sink assembly 93, and a fan(not shown in the drawings, but similar to the fan of FIGS. 2A-2B). EachLED array can be configured in the same way as is described above withreference to FIGS. 5A-5D.

The heat pipe assembly 91 includes a forward heat pipe 95, four rearwardheat pipes 97, and an intermediate heat-transfer block 99. In addition,a machined, mounting sleeve 101 having five equally sized faces 103 (seeFIGS. 8A-8C) is soldered or brazed onto the forward heat pipe 95, andthe five LED arrays 31 are mounted individually on these faces. The heatpipes 95, 97, the mounting sleeve 103, and the heat-transfer block 99preferably all are formed of a material having high heat conductivity,e.g., oxygen-free copper (C10100).

As best shown in FIGS. 9A-9C, the heat-transfer block 99 includes aforward aperture 105 for conformably receiving the rearward end of theforward heat pipe 95 and four additional apertures 107 for conformablyreceiving the forward ends of the four rearward heat pipes 97. Theheat-transfer block and the heat pipes are soldered together, to form anassembly that provides excellent heat transfer between the forward andrearward heat pipes. An additional aperture 109 is provided for carryinga cable (not shown) that provides electrical power for the LED arrays 31(FIG. 5A) and that transmits a signal representing the resistance valuemeasured by the thermistor 73 (FIG. 5A).

In an alternative embodiment (not shown in the drawings), theheat-transfer block can take the form of a mass of heat-conductivesolder or epoxy deposited into the interstices between adjacentlypositioned forward and rearward heat pipes.

The four rearward heat pipes 97 all extend rearward from theheat-transfer block 99 along axes perpendicular to the parallel fins 111of the heat sink assembly 93. The heat pipes are individually solderedto the fins at spaced-apart locations, and thus function effectively totransfer heat from the heat-transfer block to the heat sink assembly.This provides better heat transfer to the heat sink assembly than wouldembodiments having just a single rearward heat pipe. Other orientationsfor the four rearward heat pipes, or a different number of rearward heatpipes, could alternatively be provided. The forward heat pipe 95 and therearward heat pipes 97 preferably all are of conventional, off-the-shelfdesign. As with the first embodiment, those skilled in the art will knowhow to size the heat pipe assembly 91, the heat sink assembly 93, andthe fan to properly handle the amount of heat to be dissipated.

In another alternative embodiment (not shown in the drawings), theforward heat pipe could be forged to a polygonal shape, with a separateLED array 31 mounted on each face of the polygon. This would eliminatethe need for the separate mounting sleeve 101.

The aluminum-nitride substrate 69 of each LED array 31 can be reliablybonded to one face 57 of the forward end cap 51 (FIG. 4A) or mountingsleeve 101 (FIGS. 8A-8C) using a high-temperature solder (e.g., SAC305), a low-temperature solder (e.g., tin-lead, indium-silver, ortin-bismuth) to prevent reflow of the fin solder, or a B-stagedheat-conductive epoxy material (e.g., AiT RT 8550).

The preferred bonding technique, however, is shown schematically inFIGS. 10A-10B. It uses a special Nanofoil® material available from TheIndium Corporation of America, of Utica, N.Y. The Nanofoil® materialcomprises alternating layers of nickel and aluminum, in a combinedthickness of about 40 microns. This material has a coating of tin (orother solder) on both of its sides, and it is sandwiched between theoverlying aluminum-nitride substrate 69 and the underlying end cap 51(or mounting sleeve 101). The substrate's copper-plated undersurfacebears a thin (˜0.2 micron) immersion silver film, and the end cap's (ormounting sleeve's) outer surface bears a thin (˜12 micron) tin platinglayer.

The Nanofoil® material, when initiated by a heat pulse delivered from alaser pulse, electric spark, etc., undergoes a self-sustainingexothermic reaction. This produces an intermetallic compound of nickelaluminide, in solid and liquid phase only, without releasing any gas.The rapidity of the reaction (˜10 msec.) enables the bonding to becompleted before the underlying heat pipe assembly 33 (or 91) candissipate the heat. This approach also allows LED arrays 31 to beattached sequentially, and it eliminates the need to heat the entireheat sink assembly 39 and the need for a complex assembly fixture, aswould be required for conventional solder or thermal epoxy. After thereaction has been completed, the nickel-aluminide densifies, to allowthe tin from the Nanofoil's upper and lower surfaces to form a strong,gap-free bond, as shown in FIG. 10B.

With reference again to FIG. 1, the LED light engine 25 (or 89) isconfigured to provide for a controlled adjustment of the distributionpattern of the projected light beam, ranging from a flat field (FIG.11A) to a peak field (FIG. 11B). This contrasts with the fixeddistribution pattern (see FIG. 12) provided by the LED lighting fixturedescribed in the Kinzer patent application publication identified above.This field adjustment is accomplished by moving the entire LED lightengine axially relative to the reflector 27, which in turn moves the LEDarrays 31 axially relative to the reflector's near focal region. Thecontrolled movement is achieved using a threaded stud 113 projectingrearward from the rear side of the heat sink assembly 39 and a matingthreaded socket in a control knob 115 captured on the rear side of therear housing 45. The threaded stud and the control knob are sized suchthat manually turning the control knob can move the LED arrays axiallyas much as 7 mm.

In other embodiments not shown in the drawings, the forward end of theheat pipe assembly, which forms the assembly's evaporator section, couldbe made by forming the end of a tube into a generally squarecross-section (or other polygonal shape) using a suitable deep drawing,forging, or swaging process. In such embodiments, the LED arrays can bemounted directly onto the heat pipe's formed faces.

In still other embodiments not shown in the drawings, a closed-loopcooling system could be substituted for the various heat pipe assembliesdescribed above. Such a cooling system would channel a working liquidthrough a closed-loop path, picking up heat from the LED arrays anddelivering it to a heat sink before returning along a separate path backto the LED arrays. Such a closed-loop system would likely be morecomplex than a heat pipe system, but could be even more effective inconducting heat away from the LED arrays.

In yet other embodiments not shown in the drawings, the lightingfixture's concave reflector could itself function as a heat sink for theLED light engine. This could take the form of metallic fins built-in tothe reflector's backside.

In all of the embodiments described above, the LED arrays preferablynumber at least three, and they are arranged symmetrically around thelongitudinal light source axis, which aligns with the lighting fixture'slongitudinal fixture axis when the LED light engine is installed. Thisminimizes the possibility of dark regions in the projected light beam.

It should be appreciated from the foregoing description that the presentinvention provides an improved LED light engine configured to beretrofit to prior incandescent lamp lighting fixtures. The improved LEDlight engine effectively places its LED arrays in a compact arrangementsubstantially coincident with the a focal region of the fixture'sconcave reflector such that the reflector can efficiently collect andutilize the light emitted by the LEDs. In addition, the LED lightengine's configuration allows a significant proportion of the priorlighting fixture to continue to be utilized, leading to substantial costsaving. Numerous embodiments and alternative configurations for thelight engine's heat pipe assembly and heat sink assembly are described.Those skilled in the art will appreciate that various features of eachdisclosed embodiment can be combined with various features of otherembodiments.

Although the invention has been described in detail with reference onlyto the presently preferred embodiments, those skilled in the art willappreciate that various modifications can be made without departing fromthe claimed invention. Accordingly, the invention is defined only by thefollowing claims.

I claim:
 1. A light source assembly configured for attachment to alighting fixture of a type having a concave reflector and projectinglight forward along a longitudinal fixture axis, wherein the concavereflector includes a central opening aligned with the longitudinalfixture axis, the light source assembly comprising: three or more LEDassemblies; a heat sink; a heat pipe assembly having a forward end thatmounts the three or more LED assemblies and a rearward end connecteddirectly to the heat sink, wherein a portion of the heat pipe assemblyextends through the central opening of the concave reflector and definesa longitudinal light source axis, and wherein the heat pipe assemblyfurther has a single elongated, hermetically sealed interior cavityextending along substantially its entire length, with a transversedimension that is relatively small at its forward end, adjacent to theLED assemblies, and relatively large at its rearward end, adjacent tothe heat sink; and a fastener configured for attachment to the lightingfixture, with the heat sink located rearward of the concave reflector,with the light source axis aligned with the fixture axis, and with thethree or more LED assemblies located at or near a focal region of theconcave reflector; wherein, in operation, with the light source assemblyattached to the lighting fixture, light emitted from the three or moreLED assemblies is reflected by the concave reflector and projectedforward along the longitudinal fixture axis, and heat generated by theLED assemblies is conducted rearward along the heat pipe assembly to theheat sink.
 2. The light source assembly as defined in claim 1, wherein:each of the three or more LED assemblies includes a substantially planarsubstrate supporting a plurality of LEDs; the heat pipe assemblyincludes a forward end cap at its forward end and a rearward tube at itsrearward end; the forward end cap and rearward tube are secured togetherto form the single interior cavity; and the outer surface of the forwardend cap defines three or more substantially flat surfaces, each surfacesized and configured to support the substrate of a separate one of thethree or more LED assemblies.
 3. The light source assembly as defined inclaim 1, wherein: each of the three or more LED assemblies includes asubstantially planar substrate; and the heat pipe assembly furtherincludes a sleeve having a central opening sized to fit conformably overthe forward end of the heat pipe assembly, the sleeve having an outersurface that defines three or more substantially flat surfaces, eachsized and configured to support the substrate of a separate one of thethree or more LED assemblies.
 4. The light source assembly as defined inclaim 1, wherein each of the three or more LED assemblies includes asubstantially planar substrate supporting a plurality of LEDs arrangedin one or more rows having axes substantially parallel with thelongitudinal light source axis.
 5. The light source assembly as definedin claim 4, wherein: the concave reflector of the lighting fixtureincludes circumferential facets; each of the three or more LEDassemblies includes two or more rows of LEDs, with the LEDs in adjacentrows arranged in a staggered relationship relative to each other; andthe arrangement of LEDs cooperates with the circumferential facets ofthe concave reflector such that the lighting fixture projects a beam oflight having an intensity that is substantially uniformcircumferentially.
 6. The light source assembly as defined in claim 1,wherein: each of the three or more LED assemblies includes asubstantially planar substrate supporting a plurality of LEDs; the threeor more LED assemblies are substantially identical and separate fromeach other; and the three or more LED assemblies are arrangedsubstantially symmetrically around the heat pipe assembly's forward end.7. The light source assembly as defined in claim 1, wherein: thelighting fixture includes a threaded socket opening rearward; and thefastener includes a single screw sized and configured to engage thelighting fixture's threaded socket, with its head located rearward ofthe heat sink and exposed on the rearward side of the light sourceassembly.
 8. The light source assembly as defined in claim 1, wherein:the three or more LED assemblies include four identical LED assemblies,each including a substantially planar substrate supporting a pluralityof LEDs arranged in two or more rows having axes substantially parallelwith the longitudinal light source axis; and the forward end of the heatpipe assembly defines four planar surfaces, each sized and configured tosupport a separate one of the four LED assemblies.
 9. A light sourceassembly configured for attachment to a lighting fixture of a typehaving a concave reflector and projecting light forward along alongitudinal fixture axis, wherein the concave reflector includes acentral opening aligned with the fixture axis, the light source assemblycomprising: three or more LED assemblies; a heat sink; a heat pipeassembly having a rearward end operatively connected to the heat sinkand a forward end that mounts the three or more LED assemblies, whereina portion of the heat pipe assembly extends through the central openingof the concave reflector and defines a longitudinal light source axis,and wherein the heat pipe assembly includes a forward heat pipe having aforward end, a rearward end, and a single elongated, hermetically sealedinterior cavity, a plurality of rearward heat pipes, each having aforward end, a rearward end, and a single elongated, hermetically sealedinterior cavity, and a heat-transfer block mounting the rearward end ofthe forward heat pipe and the forward ends of the plurality of rearwardheat pipes, wherein the forward end of the forward heat pipe mounts thethree or more LED assemblies, and the rearward ends of the plurality ofrearward heat pipes all connect to the heat sink, and wherein thetransverse dimension of the interior cavity of the forward heat pipe issmall relative to the combined transverse dimensions of the interiorcavities of the plurality of rearward heat pipes; and a fastenerconfigured for attachment to the lighting fixture, with the heat sinklocated rearward of the concave reflector, with the light source axisaligned with the fixture axis, and with the three or more LED assemblieslocated at or near a focal region of the concave reflector; wherein, inoperation, with the light source assembly attached to the lightingfixture, light emitted from the three or more LED assemblies isreflected by the concave reflector and projected forward along thefixture axis, and heat generated by the LED assemblies is conductedrearward along the heat pipe assembly to the heat sink.
 10. The lightsource assembly as defined in claim 9, wherein the rearward ends of theplurality of rearward heat pipes have longitudinal axes arrangedsubstantially parallel with the longitudinal light source axis andconnect to the heat sink at spaced-apart locations.
 11. The light sourceassembly as defined in claim 9, wherein: each of the three or more LEDassemblies includes a substantially planar substrate; and the heat pipeassembly further includes a sleeve having a central opening sized to fitconformably over the forward end of the forward heat pipe, the sleevehaving an outer surface that defines three or more substantially flatsurfaces, each sized and configured to support the substrate of aseparate one of the three or more LED assemblies.
 12. The light sourceassembly as defined in claim 9, wherein: the three or more LEDassemblies include four identical LED assemblies, each including asubstantially planar substrate supporting a plurality of LEDs arrangedin two or more rows having axes substantially parallel with the lightsource axis; and the forward end of the forward heat pipe defines foursubstantially flat surfaces, each sized and configured to support aseparate one of the four LED assemblies.
 13. The light source assemblyas defined in claim 12, wherein each of the four LED assemblies includesa solder layer bonding the substantially planar substrate to a separateone of the four substantially flat surfaces at the forward end of theforward heat pipe.
 14. The light source assembly as defined in claim 9,wherein each of the three or more LED assemblies includes asubstantially planar substrate supporting a plurality of LEDs arrangedin one or more rows having axes substantially parallel with thelongitudinal light source axis.
 15. The light source assembly as definedin claim 14, wherein: the concave reflector of the lighting fixtureincludes circumferential facets; each of the three or more LEDassemblies includes two or more rows of LEDs, with the LEDs in adjacentrows arranged in a staggered relationship relative to each other; andthe arrangement of LEDs cooperates with the circumferential facets ofthe concave reflector such that the lighting fixture projects a beam oflight having an intensity that is substantially uniformcircumferentially.
 16. The light source assembly as defined in claim 9,wherein: each of the three or more LED assemblies includes asubstantially planar substrate supporting a plurality of LEDs; the threeor more LED assemblies are substantially identical and separate fromeach other; and the three or more LED assemblies are arrangedsubstantially symmetrically around the forward heat pipe's forward end.17. The light source assembly as defined in claim 9, wherein: thelighting fixture includes a threaded socket opening rearward; and thefastener includes a single screw sized and configured to engage thelighting fixture's threaded socket, with its head located rearward ofthe heat sink and exposed on the rearward side of the light sourceassembly.
 18. The light source assembly as defined in claim 9, whereinthe heat-transfer block includes a forward aperture for conformablyreceiving the rearward end of the forward heat pipe and a plurality ofrearward apertures for conformably receiving the forward ends of theplurality of rearward heat pipes.
 19. A lighting fixture comprising: aconcave reflector having a central opening aligned with a longitudinalfixture axis; and a light source assembly configured for attachment tothe concave reflector, the light source assembly comprising three ormore LED assemblies, a heat sink, a heat pipe assembly having a forwardend that mounts the three or more LED assemblies and a rearward endconnected directly to the heat sink, wherein a portion of the heat pipeassembly extends through the opening of the concave reflector anddefines a longitudinal light source axis, and wherein the heat pipeassembly further has a single elongated, hermetically sealed interiorcavity extending along substantially its entire length, with atransverse dimension that is relatively small at its forward end,adjacent to the LED assemblies, and relatively large at its rearwardend, adjacent to the heat sink, and a fastener configured for attachmentto the lighting fixture, with the heat sink located rearward of theconcave reflector, with the light source axis aligned with the fixtureaxis, and with the three or more LED assemblies located at or near afocal region of the concave reflector; wherein, in operation, with thelight source assembly attached to the concave reflector, light emittedfrom the three or more LED assemblies is reflected by the concavereflector and projected forward along the longitudinal fixture axis, andheat generated by the LED assemblies is conducted rearward along theheat pipe assembly to the heat sink.
 20. A light source assemblyconfigured for attachment to a lighting fixture of a type having aconcave reflector and projecting light forward along a longitudinalfixture axis, wherein the concave reflector includes a central openingaligned with the longitudinal fixture axis, and wherein the lightingfixture further includes a threaded socket opening rearward, the lightsource assembly comprising: three or more LED assemblies; a heat sink; aheat pipe assembly having a forward end that mounts the three or moreLED assemblies and a rearward end connected directly to the heat sink,wherein a portion of the heat pipe assembly extends through the centralopening of the concave reflector and defines a longitudinal light sourceaxis, and wherein the heat pipe assembly further has one or moreelongated, hermetically sealed interior cavities, with a transversedimension that is relatively small at its forward end, adjacent to theLED assemblies, and relatively large at its rearward end, adjacent tothe heat sink; and a fastener configured for attachment to the lightingfixture, with the heat sink located rearward of the concave reflector,with the light source axis aligned with the fixture axis, and with thethree or more LED assemblies located at or near a focal region of theconcave reflector, wherein the fastener includes a single screw sizedand configured to engage the lighting fixture's threaded socket, withits head located rearward of the heat sink and exposed on the rearwardside of the light source assembly; wherein, in operation, with the lightsource assembly attached to the lighting fixture, light emitted from thethree or more LED assemblies is reflected by the concave reflector andprojected forward along the longitudinal fixture axis, and heatgenerated by the LED assemblies is conducted rearward along the heatpipe assembly to the heat sink.